As is known, the usual heat pump used to heat buildings, for example, includes an electrically-driven compressor, a throttling valve, an evaporator located in the ambient atmosphere outside the building, and a condenser within the building which discharges heat as a refrigerant is condensed. Such systems are relatively complicated, have low coefficients of performance based upon actual thermal conversion and, of course, require a liquid refrigerant which tends to be expensive and may have toxic properties. Furthermore, the energy input into the system is usually electrical and, hence, does not utilize the heat rejected in the electrical energy production.